The present invention relates to a vehicle steering system for controlling a steering or steering lock angle of at least one wheel of a vehicle having a steering handle, in particular a steering wheel, with a detection device being provided for recording the degree of actuation of the steering handle, with a mechanical actuation link being provided between the steering handle and at least one steered vehicle wheel, with an actuator being provided to provide supported adjustment of the steering or steering lock angle, and with a control device being provided for the actuator, whereby the actual manual torque or force that is to be applied by the driver for controlling the vehicle being regulated by the control device as a function of the vehicle condition or state values.
With hydraulic power-assisted steering systems, as a rule a control valve controls an oil pressure in the steering cylinder in a manner corresponding to the rotary movement of the steering wheel. An elastic torque-measuring element, such as a torsion bar, helical spring, or leaf spring, converts the torque engaging at the steering wheel into a control travel movement. By means of the control travel, control edges designed as bevelled or chamfered elements or facets are displaced, and so form the corresponding aperture cross-section for the oil flow.
With power-assisted steering systems in which the supporting torque is created by means of an electric motor as an actuator, a torque-measuring device likewise serves as a rule for measuring the manual torque applied by the driver.
Increasing demands with regard to the operating convenience of power-assisted steering and the safety of the vehicle have led to the introduction of parameterable power-assisted steering systems. These work, for example, as a function of the speed; i.e. the travel speed displayed by the electronic tachometer controls or influences the actuation force to be applied to the steering wheel or the steering handle by the driver. A control device assesses the speed signals and determines the value of the supporting torque to be adjusted, which is required by the actuator to provide the supportive setting of the steering or steering lock angle. In this way, the special design of the steering characteristics can lead to the situation in which, when carrying out parking maneuvers and when turning the steering wheel while stationary, only minimal force is to be applied to the steering wheel, while with increasing speed of the vehicle the amount of the assistance force and assistance torque is reduced. Accordingly, at high speeds exact and precisely-aimed steering is made possible.
A disadvantage of the known power-assisted steering systems is the fact that the manual torque applied to the steering handle or steering wheel is measured and only passed on to the actuator device with amplification. As a result of this, only an inadequate degree of operating comfort and convenience is attained. With these systems, as a rule, the active return, i.e. the return of the released steering wheel to the central setting, is implemented explicitly by means of an additional control device, as a result of which the entire regulation/control of the system is complicated and prone to failure. The implementation of active damping or attenuation can only be achieved in the conventional systems with substantial effort and in most cases is unsatisfactory. In addition, a disadvantage of these systems that friction compensation, i.e. the taking into consideration of the friction present in the steering system, may not be considered, or only insufficiently. By the implementation of the options referred to above, the controller is in most cases so complex that it can only be optimized with great effort, if at all.
The object of the present invention is to provide a vehicle steering system which is easier to optimize, in which the manual torque to be applied by the driver can be predetermined and, in particular, can be precisely adjusted.